Potential Benefit of Combining Heat Pumps with Solar Thermal for Heating and Domestic Hot Water Preparation

Abstract

In this work, the combination of solar thermal systems with heat pumps has been numerically analyzed. Potential benefits have been studied by comparing systems that use only a heat pump with combined systems. All simulations were carried out with Polysun-6® for several climates around Europe. The simulated systems are designed to provide space heat and domestic hot water for single family houses. Results presented in this work show that the seasonal performance factor of the overall heating system increases when a solar thermal system is added for both air source and ground source heat pumps. The performance of the ground source heat pump alone also tends to increases when it is combined with a solar thermal system. On the other hand, the performance of the air source heat pump alone decreases when it is combined with a solar thermal system. For this reason, in terms of fractional electricity savings, the potential benefit of ground source based systems is higher than that of an air source heat pump. Obviously the energetic benefit also increases with collector area and solar radiation. In terms of absolute electricity savings, the benefit of adding solar thermal to a heat pump system increases with the electric energy consumption of the reference system without the solar thermal part. Therefore air source systems have usually higher potential compared to ground source based systems despite of the lower fractional electricity savings. For the same reason, systems with high energy demand, e.g. systems in colder climates or with lower building insulation standard; will also benefit more than those of low energy demand. The optimum climate in terms of absolute electricity savings is found in a typical alpine location with cold climate but at the same time high irradiation in winter.